T. rex didn't need proper arms thanks to its neck

Tyrannosaurus rex was the most terrifying animal that ever lived, apart from its silly little arms, which were no use for anything. Now it seems this giant predator did not need proper arms, because its head and neck were so powerful.

Tyrannosaurs, the family of big predatory dinosaurs that includes T. rex, had necks that were similar to those of modern birds. So by studying how birds feed, Eric Snively of the University of Wisconsin–La Crosse and his colleagues were able to reconstruct how T. rex went about making a kill.

"We looked at a number of raptors and documented their behaviour," says Snively. "There is a strong possibility that the tyrannosaurs behaved in the same way."

Snively placed electrodes on the skin of a dozen birds from 10 different species, ranging from domestic chickens to bald eagles. That allowed him to identify the precise muscle movements underlying each stage of feeding.

Shake and snap

Snively found that the birds often raised their heads and fixed their vision on the prey before lowering their heads to attack. T. rex had most of the same muscles, suggesting it could perform the same movements. That would also include raising its head, thrusting it upwards and pulling back with its legs once it has taken a bite.

Many of the birds also shook their necks, and the main muscle involved was found in the necks of tyrannosaurs. "The shaking motion is the same as when a dog shakes off water," says Snively. "We think that the dinosaur would have used this motion to dislodge meat from a carcass."

Their powerful necks could explain why tyrannosaurs had such small arms, says Snively. "Tyrannosaurs didn't need big arms to hunt, because their powerful bites and hyper-bulldog necks did the job," he says. "From the shoulders forward, T. rex was like a whole killer whale: just bite, shake and twist."

Tyrannosaur necks are also similar to crocodile necks. "We can think of them as striking like a bird, and shake-feeding like a crocodile," says Snively.

The results are promising, says David Hone of Queen Mary University of London. "We need to be careful not to overly rely on these as analogies, but in at least some ways, some animals like tyrannosaurs that are relatively distant from birds are still very bird-like."

If you would like to reuse any content from New Scientist, either in print or online, please contact the syndication department first for permission. New Scientist does not own rights to photos, but there are a variety of licensing options available for use of articles and graphics we own the copyright to.